Within hoes and small businesses there is a proliferation of telecommunication terminals connected to a single telephone link. Although, ISDN links have been introduced into the telecommunication public network, the vast majority of small businesses and private homes are still served by analog telephone links. Even in the average hone, one finds a plurality of telephones, answering machines, computers, and fax machines; all of which are connected to a single analog telephone link. In addition, the public utility provider of water, electricity, and natural gas have long wanted to red the utility meters measuring the usage of these three items via telephone links without having to install dedicated links or to utilize an existing telephone link that alerted the customers in their homes. Further, the public utility companies could use control over electrical consumption within homes to do load averaging. Finally, whereas it is convenient to have a plurality of telephone sets each connected to a single analog telephone link, it would be desirable if a caller could preselect one of those telephone sets and only that telephone set would ring for the incoming call from the caller.
ISDN basic rate interface (BRI) links could potentially solve many of the problems set forth in the previous paragraph; however, it will be many years before ISDN BRI links replace any sizable portion of the existing analog telephone links. This is largely true because of the large amount of customer owned telephone equipment.
Within the prior art, incoming calling line identification (ICLID) data messages are transmitted during the silent intervals of the ringing on an analog telephone link of an incoming call. However, ICLID data messages only contain information related to the identity of the calling party. U.S. Pat. No. 4,582,956 discloses a device for extracting the telephone number or other source information from an ICLID data message and displaying that information to the called party. In addition, U.S. Pat. No. 5,228,080 discloses using a data message that consists of the word "private" to stop the called telephone set from ringing and to provide a voice message back to the calling party informing that party that the called party does not accept calls from individuals who wish to keep their identity unknown. The word "private" is transmitted as the ICLID message when the caller does not want their identity known. Other systems have made similar use of the identification of the calling party.